Wireless communication systems are widely deployed to provide various types of communications such as voice, data, video, etc. These systems may be multiple-access systems capable of supporting communication with multiple access terminals by sharing available system resources (e.g., bandwidth, transmit power etc.) Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems or combinations thereof. Typically, a wireless communication system comprises several base stations, wherein each base station communicates with a mobile station using a forward link and each mobile station (or access terminal) communicates with base station(s) using a reverse link.
When data is generated for transmission by a user, a service request is transmitted via established communication channels from a user equipment/access terminal to a serving base station and based on negotiated service options/availability, resources are assigned to the user. Most modern wireless communication systems have a mix of users carrying different types of traffic flows. This necessitates different mechanisms to assign the physical channel resources (bandwidth, time etc.) to different users. Typically, in a synchronous system with centralized scheduling, the receiver's data is broken into packets which are coded independently, and the receiver's channel assignment lasts at least for the duration of the packet. This duration itself may be fixed or may vary depending on feedback from the receiver. But after this duration, one approach is to keep the assignment until it is explicitly terminated or reassigned to another user—such assignments are called ‘sticky’. Another approach is to say that each assignment lasts only for the packet duration—such assignments are called ‘non-sticky’.
Therefore, for users who need an assigned communication resource for longer periods of time, sticky assignments make it unnecessary to keep reassigning the resource to them. This potentially reduces their latency as well as reducing the signaling overhead on the control channel that carries the user assignments. Further, it allows the system to support a situation where there are a large number of users, each needing a small bandwidth for a long time period (e.g. voice users), without overloading this control channel. However, it makes it necessary to include in the control channel signaling, ways to inform the owner of termination of a sticky assignment, e.g., either by a reassigning the resource to another user (in which case, the control signal must be heard by both the current and the new user) or by an explicit deassignment message to the current user. Additionally, in order to maintain the usefulness of sticky assignments for the above-mentioned situation with a large number of voice users, it is necessary to allow users to hold sticky assignments even when there is no data to send them. This necessitates a mechanism to let each user know at any given time whether their sticky assignment is carrying data or not. Accordingly, a transmitter sends a known sequence, called an ‘erasure sequence’, which the receiver will attempt to detect to decide whether or not a frame corresponds to the start of a packet or to an erasure.
However, the erasure sequences have to be detected within a short time period e.g., one frame. Additionally, the erasure detection process cannot obtain gains from H-ARQ (Hybrid Automatic Repeat Request) procedure while coding across multiple frame durations. This makes erasure detection harder than normal packet demodulation.